Controller circuits are used nowadays in many applications primarily in industry and in traction applications, for example in the railroad sector. A controller circuit for converting a first DC voltage into a second DC voltage is specified for example in DE 197 50 041 C1, wherein the controller circuit comprises a step-up controller and a converter connected downstream of the step-up controller on the output side, in particular in a half-bridge circuit, the converter having a DC voltage circuit formed by capacitive energy stores and being connected to the secondary side of a transformer via an inductor on the output side. Furthermore, the controller circuit comprises a rectifier, which is connected to the secondary winding of the transformer on the input side. The step-up controller and the converter in DE 197 50 041 C1 are driven in such a way that the capacitive energy stores, the inductor and the leakage inductance of the transformer form a resonant tuned circuit, that is to say that the step-up controller, on the output side, applies a corresponding AC voltage to the capacitive energy stores by clocking the DC voltage at its input, such that the resonant tuned circuit is caused to attain resonance.
What is problematic about a controller circuit mentioned above is that despite the resonant tuned circuit described above, switching losses can still occur in the power semiconductor switches of the converter, and subject said switches to a high degree of loading, in particular thermal loading. As a result, the power semiconductor switches age correspondingly rapidly and the failure rates of the power semiconductor switches rise with the operating period of the controller circuit. A high availability of the controller circuit, such as is essential in traction applications, for example, is then no longer afforded.
U.S. Pat. No. 6,344,979 B1 likewise specifies a controller circuit in FIG. 4, for example, comprising a resonant converter, a transformer, a rectifier, which rectifier is connected to the secondary winding of the transformer on the input side, and a CLL resonant circuit connected to the resonant converter and to the primary winding of the transformer, which CLL resonant circuit has a resonance capacitance and a first and a second resonance inductance. As discussed, DE 197 50 041 C1 and U.S. Pat. No. 6,344,979 B1 have these observed drawbacks.